It is well known that an optical system and an imaging element are widely used by being mounted in a digital camera or video camera. If the position and orientation at which the imaging element is attached is shifted from the desired position and orientation relative to the optical system, the desired image cannot be obtained. Therefore, the imaging element needs to be attached to a high degree of accuracy at the desired position and orientation relative to the optical system. To this end, there are known techniques for attaching an imaging element at a desired position relative to the optical system.